Degradation of transparent conductive oxides: mechanistic insights across configurations and exposures

Understanding transparent conductive oxide (TCO) degradation is critical to improving stability and lifetime of both organic and inorganic thin lm PV modules, which utilize TCOs, like indium tin oxide (ITO), aluminumdoped zinc oxide (AZO) and uorine-doped tin oxide (FTO) as electrodes. These TCOs must retain their long-term functionality in diverse outdoor environments. In addition to bulk material degradation, interfacial degradation, a frequent avenue for failure in PV systems, is promoted by exposure to environmental stressors such as irradiance, heat and humidity. ITO, AZO and FTO samples in an open-faced con guration were exposed to damp heat and ASTM G154 for up to 1000 hours. The e ect of exposure on electrical and optical properties and surface energies of cleaned samples was measured. Yellowness, haze, water contact angle and resistivity of the di erent materials trended di erently with exposure time and type, indicating the activation of distinct degradation mechanisms. An encapsulated con guration study was conducted on ITO and AZO, exposing samples to the above accelerated exposures and two outdoor exposures (1x suns and 5x suns on a dual axis trackers), with and without PEDOT:PSS layers. PEDOT:PSS increases the yellowness and haze of ITO and AZO, but does not accelerate the increase in resistivity, suggesting that the optical and electrical degradation mechanisms are not coupled. Additionally, the hazing/roughening mechanism of PEDOT:PSS on AZO appears to be photo-sensitive; 5x outdoor exposure samples demonstrated distinctly higher haze than damp heat exposed samples.

[1]  Bernd Rech,et al.  Damp heat stability and annealing behavior of aluminum doped zinc oxide films prepared by magnetron sputtering , 2006 .

[2]  M.J.A. de Voigt,et al.  Stability of the interface between indium-tin-oxide and poly(3,4-ethylenedioxythiophene)/poly(styrenesulfonate) in polymer light-emitting diodes , 2000 .

[3]  C. G. Allen,et al.  Surface modification of ZnO using triethoxysilane-based molecules. , 2008, Langmuir : the ACS journal of surfaces and colloids.

[4]  Neal R Armstrong,et al.  Modification of Transparent Conducting Oxide (TCO) Electrodes through Silanization and Chemisorption of Small Molecules , 2007 .

[5]  P. Blom,et al.  Degradation mechanisms in organic photovoltaic devices , 2012 .

[6]  Zhiqiang Gao,et al.  Blocking reactions between indium-tin oxide and poly (3,4-ethylene dioxythiophene):poly(styrene sulphonate) with a self-assembly monolayer , 2002 .

[7]  Helmut Stiebig,et al.  Transparent conducting oxide films for thin film silicon photovoltaics , 2007 .

[8]  Neelkanth G. Dhere,et al.  Design of high-reliability low-cost amorphous silicon modules for high energy yield , 2008, Optics + Photonics for Sustainable Energy.

[9]  Rommel Noufi,et al.  An Investigation of Stability Issues of ZnO and Mo on Glass Substrates for CIGS Solar Cells upon Accelerated Weathering and Damp Heat Exposures , 2007 .

[10]  M. Rusu,et al.  Role of ITO and PEDOT:PSS in stability/degradation of polymer:fullerene bulk heterojunctions solar cells , 2010 .

[11]  F. J. Pern,et al.  Stability of TCO window layers for thin-film CIGS solar cells upon damp heat exposures: part II , 2009, Optics + Photonics for Sustainable Energy.

[12]  Michael D. Kempe,et al.  Stress Induced Degradation Modes in CIGSS Minimodules (Presentation) , 2008 .

[13]  Charlie Wood,et al.  Examination of lifetime-limiting failure mechanisms in CIGSS-based PV minimodules under environmental stress , 2008, 2008 33rd IEEE Photovoltaic Specialists Conference.

[14]  Y. C. Chan,et al.  A study of degradation of indium tin oxide thin films on glass for display applications , 2013 .

[15]  J. Adelstein,et al.  Accelerated Stress Testing of Thin-Film Modules with SnO2:F Transparent Conductors , 2003 .

[16]  Reiner Klenk,et al.  Damp heat stability of Al-doped zinc oxide films on smooth and rough substrates , 2011 .